I'm a PS3 owner, but I must say, Halo is just much more fun than Killzone. Killzone's campaign and multyplayer are great, I really liked the game but wasn't as good as I expected.. besides, what's the point in having bots offline, without split-screen, specially if you have an awesome Online? Imo, Halo is just better to play with friends. If Killzone 2 gets Split-Screen, just like UT3 got, then my opinion would radically change. Till then, my vote goes for Halo.